1. Field of the Invention
The present invention relates to an ink suitable for use in, particularly, ink-jet recording in which an ink is ejected from an orifice in response to recording signals to conduct recording on a recording medium, and an ink set, ink cartridge, recording unit, image recording apparatus and image recording process using
2. Related Background Art
Inks with various compositions have heretofore been reported and proposed for inks to be used for ink-jet recording. In particular, in recent years, detailed research and developments have been made from various approaches such as composition and physical properties of inks so that a good record can be made even on plain paper such as paper for copying, paper for reporting, notepaper and letter paper, which are commonly used in offices, or even on cloth.
Various systems have also been proposed for ink-jet recording methods, including a system wherein charged ink droplets are continuously ejected to use a part thereof for recording, a system wherein signals are given to a recording head having a piezoelectric element, and an ink is ejected in response to the signals to conduct recording, a system wherein thermal energy according to recording signals is applied to an ink within a recording head by means of, for example, a heater, and the ink is ejected by the thermal energy to conduct recording, etc. Such an ink-jet recording method using a system wherein an ink is ejected by the bubbling phenomenon of the ink caused by thermal energy as described in, for example, Japanese Patent Application Laid-Open No. 54-59936 is a main system for ink-jet recording methods at present from the view point that high integration and high density assembly of openings from which an ink is ejected (hereinafter referred to as xe2x80x9corificesxe2x80x9d) are conducted with ease. By the way, examples of preferred characteristics or properties that inks used in ink-jet recording should have include the following characteristics or properties:
(1) providing clear or bright images having a high optical density;
(2) providing high-quality images free of any undefined or irregular feathering;
(3) having high fixing ability to recording media;
(4) being excellent in ejection stability; and
(5) having good storage stability.
With the demands for further speeding up of printing, multi-coloring of images, still higher definition of images and still higher image quality in recent years, recording media of various types have also been developed according to their application fields, and there is thus the demand for development of inks which meet the above-described characteristics (1) to (3) at a higher level irrespective of recording media and moreover satisfy the above-described characteristics (4) and (5) at a high level.
In response to such a demand, for example, Japanese Patent Application Laid-Open No. 6-271798 discloses an ink comprising bis(hydroxyethyl)sulfone (hereinafter abbreviated as xe2x80x9cBHESxe2x80x9d) as an ink satisfying the provision of high-quality images, good fixing ability to recording media and good ejection stability scarcely causing clogging at an orifice.
As the results of investigations carried out by the present inventors up to this time, the following findings have been obtained.
Namely, when a water-based ink containing no BHES is used in the system wherein the ink is ejected by means of a heater, kogation derived from a water-soluble coloring material in the ink gradually occurs on the heater, and this kogation prevents stable ejection of the ink and moreover adversely affects the formation of high-quality images.
In addition, the addition of BHES to the water-based ink can effectively prevent the occurrence of kogation derived from the water-soluble coloring material on the heater.
Under such circumstances, the present inventors have carried out further investigation as to inks containing a water-soluble coloring material and BHES in an aqueous medium with a view toward further improving the above-described characteristics. As a result, it has been found that when the pH of such an ink is adjusted to 9.5 to 12, particularly, 9.5 to 11, the effect of preventing the occurrence of kogation on the heater is more enhanced, and such adjustment is also effective for improvement in the storage stability of the ink, particularly, storage stability at a lower temperature.
The present invention has been completed on the basis of such findings, and it is an object of the present invention to provide an ink capable of satisfying the above-described characteristics (1) to (5) at a higher level, more specifically, for example, an ink permitting the stable formation of high-quality images on a wide variety of recording media, and having excellent ejection stability, ejection durability and storage stability.
Another object of the present invention is to provide an image recording process which permits the stable recording of high-quality images on a wide variety of recording media.
A further object of the present invention is to provide an image recording apparatus which permits the stable recording of high-quality images on a wide variety of recording media, and an ink cartridge, ink set and recording unit which can be used in such an apparatus.
A still further object of the present invention is to provide an ink capable of satisfying the above-described characteristics (1) to (5) at a higher level, more specifically, for example, an ink which permits the stable provision of high-quality images on a wide variety of recording media, has excellent ejection stability, ejection durability and storage stability, and is unlikely to cause clogging at an orifice after stopping recording for a while, even under various use environments, or even in the case where orifices are made minuter.
A yet still further Object of the present invention is to provide an image recording process by which high-quality images can be stably recorded on a wide variety of recording media, and high-quality images can be stably formed even under various use environments, or such an effect can be stably exhibited even in the case where orifices of a recording head are made minuter for the purpose of providing higher-quality images.
A yet still further object of the present invention is to provide an image recording apparatus by which high-quality images can be stably recorded on a wide variety of recording media, and high-quality images can be stably formed even under various use environments, or such an effect can be stably exhibited even in the case where orifices of a recording head are made minuter for the purpose of providing higher-quality images, and an ink cartridge, ink set and recording unit which can be used in such an apparatus.
The above objects can be achieved by the present invention described below.
According to the present invention, there is thus provided an ink comprising a water-soluble coloring material and bis(hydroxyethyl)sulfone in an aqueous medium and having a pH of from 9.5 to 12.
According to the present invention, there is also provided an image recording process, comprising the step of applying an ink comprising a water-soluble coloring material and bis(hydroxyethyl)sulfone in an aqueous medium and having a pH of from 9.5 to 12 to the image forming region of a recording medium.
According to the present invention, there is further provided an image recording apparatus, comprising a recording unit which has an ink container portion charged therein with an ink comprising a water-soluble coloring material and bis(hydroxyethyl) sulfone in an aqueous medium and having a pH of from 9.5 to 12, a means for applying the ink to a recording medium, and a means for feeding the ink to the first mentioned means, and a means for actuating the means for applying the ink to the recording medium in the recording unit in response to recording signals.
According to the present invention, there is still further provided an ink set, comprising in combination an ink comprising a first water-soluble coloring material and bis(hydroxyethyl)sulfone and having a pH of from 9.5 to 12, and another ink comprising a second water-soluble coloring material, wherein each of the first and second water-soluble coloring materials is a coloring material of a color selected from the group consisting of yellow, magenta, cyan, black, red, blue and green.
According to the present invention, there is yet still further provided an ink cartridge, comprising an ink container portion charged therein with an ink comprising a water-soluble coloring material and bis(hydroxyethyl)sulfone in an aqueous medium and having a pH of from 9.5 to 12.
According to the present invention, there is yet still further provided a recording unit, comprising an ink container portion charged therein with an ink comprising a water-soluble coloring material and bis(hydroxyethyl)sulfone in an aqueous medium and having a pH of from 9.5 to 12, a means for applying the ink to a recording medium, and a means for feeding the ink to the first mentioned means.
According to the present invention, there is yet still further provided an image recording process, comprising the step of applying an ink comprising a water-soluble coloring material, bis(hydroxyethyl) sulfone and urea in an aqueous medium and having a pH of from 9.5 to 12 to the image forming region of a recording medium by means of an image recording apparatus comprising a recording unit, which has an ink container portion charged therein with the ink, a recording head equipped with a means for ejecting the ink to a recording medium from an orifice of the size that 0.1 to 40 picoliters of the ink can be ejected by one ejection operation and a means for feeding the ink to the recording head, and a means for actuating the recording unit in response to recording signals.
According to the present invention, there is yet still further provided an image recording apparatus, comprising a recording unit, which has an ink container portion charged therein with an ink comprising a water-soluble coloring material, bis(hydroxyethyl)sulfone and urea in an aqueous medium and having a pH of from 9.5 to 12, a recording head equipped with a means for ejecting the ink to a recording medium from an orifice of the size that 0.1 to 40 picoliters of the ink can be ejected by one ejection operation and a means for feeding the ink to the recording head, and a means for actuating the recording unit in response to recording signals.
According to the present invention, there is yet still further provided a recording unit, comprising an ink container portion charged therein with an ink comprising a water-soluble coloring material, bis(hydroxyethyl)sulfone and urea in an aqueous medium and having a pH of from 9.5 to 12, a recording head equipped with a means for ejecting the ink to a recording medium from an orifice of the size that 0.1 to 40 picoliters of the ink can be ejected by one ejection operation and a means for feeding the ink to the recording head.
Incidentally, Japanese Patent Application Laid-Open No. 10-768 discloses an ink comprising a disperse dye, a compound for dispersing the disperse dye, and an aqueous liquid medium, wherein BHES is added to the ink, and the pH of the ink is adjusted to 7 to 9. However, this publication neither discloses the technical subjects related to the present invention nor describes any suggestion as to these subjects.
The action of the present invention will hereinafter be described. As described above, the present inventors have carried out investigations on ink comprising a water-soluble coloring material and BHES. As a result, it has been newly found that when the pH of such an ink is adjusted to 9.5 to 12, the occurrence of kogation on a heater can be prevented extremely effectively, and the storage stability of the ink is also improved, thus leading to completion of the present invention. Aggregation of the coloring material of this ink is scarcely observed even after the long-term storage thereof, the performance of the ink is stable, and excellent colored images can be stably provided on a wide variety of recording media. For some particular coloring materials, the storage stability of an ink containing such a coloring material may be improved in an alkaline region, since the solubility of the coloring material is enhanced. However, the effects found by this investigation have been clearly beyond the dependency on coloring materials. The reason why the above effects are brought about by such a composition is not clear. However, inferring from the structure of BHES, it is considered that interaction between the coloring material and BHES is greatly enhanced in the ink the pH of which has been adjusted to 9.5 to 12, and so the mutual association of the water-soluble coloring material dissolved in the aqueous medium is effectively prevented.